Scattering and intrinsic attenuation in Cairo metropolitan area using genetic algorithm

摘要

A total number of 46 local earthquakes (2.0 :5_ ML <4.0) recorded in the period 2000-2011 by the Egyptian seismographic network (ENSN) were used to estimate the total (Qt-1), intrinsic (Qi-1) and scattering attenuation (Q;1) in Cairo metropolitan area, Egypt. The inultiple lapse time window analysis (MLTWA) under the assumption of multiple isotropic scattering with uniform distribution of scatters was firstly applied to estimate the pair of 4- I, the extinction length inverse, and Bo, the seismic albedo, in the frequency range 3-24 Hz. To take into account the effect of a depth-dependent earth model, the obtained values of B0 and 4-1 were corrected for an earth structure characterized by a transparent upper mantle and a heterogeneous crust. The estimated values of 01 1, (2,-1 and (2,:- I exhibited frequency dependences. The average frequency-dependent relationships of attenuation characteristics estimated for the region are found to be: Qt-1=(0.015 + o.008)f(-1.02 0.02), I = (0.006 + 0.02), and Qi-1=(0.009 0.008) f (-1.o3 0.02); showing a predominance of intrinsic absorption over scattering attenuation. This finding implies that the pore-fluid contents may have great effect on the attenuation mechanism in the upper crust where the River Nile is passing through the study area. The obtained results are comparable with those obtained in other tectonic regions. (C) 2014 Elsevier Ltd. All rights reserved.